Variable-speed friction gears



June 4, 1957 E. FROST VARIABLE-SPEED FRICTION GEARS 4 Sheets-Sheet 1Filed Nov. 2, 1951 mam a Inventor iii 3% June 4, 1957 E. FROST 2,794,346

VARIABLE-SPEED FRICTION GEARS Filed Nov. 2, 1951 4 SheetsSheet 2 dcbabcdL I V y G H h q'f'efqh w I l lfl FIG-4.

d bdb f Inventor Me 'aaZ' June 4, 1957 FROST 2,794,346

VARIABLESPEED FRICTION GEARS Filed Nov. 2, 1951 4 Sheets-Sheet 3Inventor June 4, 1957 E. FROST VARIABLE-SPEED FRICTION GEARS 4SheetsSheet 4 Filed Nov. 2 1951 5" llnwllmnud Inventor United StatesFatent 6 2,794,346 VARIABLE-SPEED FRICTION GEARS Edward Frost, Wain Bay,Suva, Fiji Application November 2, 1951, Serial No. 254,596

Claims priority, application Great Britain 7 November 3, 1%50 12 Claims.(Cl. 74 -199) The present invention relates to variable speed frictiongears and, more particularly, those of the kind basically employing arotary driving disc, a rotary driven disc spaced therefrom, and a rotaryintermediate disc arranged to contact frictionally the driving anddriven discs to transmit the drive between them, the speed transmissionratio being variable by moving the position of the intermediate discrelatively to the others so that these latter will each contact theworking face of the intermediate disc at an adjusted position. It is tobe noted that where reference is made above, and in the followingspecification, to a disc this term is intended to include equivalentrotary members, e. g. spoke-provided or other forms of annulus, capableof fulfilling the functions to be hereinafter explained.

The improved gear according to the present invention is of the kind setforth above and is characterised by the fact that the contact face ofthe intermediate disc is of domed form (i. e. is of curved convex formin all diametral planes thereof) and that the driving and driven discsare arranged to make point contact with this domed face.

In constructing such a gear to operate under optimum conditions, theintermediate disc is mounted for rocking about a predetermined center,when moved for varying the transmission ratio, and it is arranged sothat the points of contact between the driving and driven discs and theintermediate disc are maintained in the same plane as this center, inall positions.

An intermediate disc contact face fulfilling the required function is asurface of revolution produced by a curve representing the intersectionof a series of equally spaced arcs, described about the said center,each in turn with successive, equi-angularly-spaced radii from saidcenter, and an appropriate shape can therefore be obtained followingthis requirement.

The aforesaid center may be a pivot point or fulcrum on which theintermediate disc is mounted for rocking movement in any direction(thus, in universal fashion). An equivalent arrangement comprises theprovision of the disc'with a part-spherical seating on a correspondingmounting, the center of the sphere representing, in this latter case,the center referred to.

Other alternative mountings fulfilling the requisite condition, whichmay be employed are, for instance, spring mountings of various forms,resilient mountings in rubber or like material, and trunnion mountings.

It will also be'understood that various forms of gear can be developedfrom the above principles (and examples will-hereinafter be described)including the use of a pair of intermediate discs in conjunction withone driving and one driven di'sc, and'a'plurality of transmission setsin a single gear.

Other constructional features of the invention will be describedhereinafter.

Several constructional forms of the invention are shown, by Way ofexample, on the accompanying drawings, wherein:

Figure 1 is an elevation of a simple construction and is intended mainlyto illustrate the principle of the inven tion;

Figure 2 is an end elevation; I

Figure 3 is a section on the line AA in Figure 1, but showing theintermediate disc adjusted laterally to a different working position;

Figure 4 illustrates a method of determining the contour of the workingface of the intermediate disc;

Figure 5 is an elevation of a modified construction which comprises asingle pair of opposed, co-operating intermediate discs between whichthe driving and driven discs are frictionally engaged;

Figure 6 is a sectional on the line BB in Figure 5;

Figure 7 is a part sectional plan view of a modified construction whichcomprises a number of driving/ driven disc pairs, each associated withtwo opposed, cooperating intermediate. discs;

Figure 8 is an elevation, struction of epicyclic type.

Figure 9 is a section on the line CC in Figure 8 but with a portion ofthe end plate of the driving machine included.

Referring first to Figures 1 to 3:

The simple constructional form of the invention shown in these figurescomprises an angle support 1, in the vertical flange 2 of which two and4 are rotatably carried. A driving disc 5 is fixed upon one of theshafts, say the shaft 3, and a driven disc 6 is fixed upon the othershaft 4. The base of the support is provided with longitudinal guideways7 which are disposed at right angles to the axes of the two shafts. Acarriage 8 is slidably mounted upon the guideways and can be adjusted toand fro along the same by means of a longitudinal threaded rod which isfitted with an operating handle 9 and is engaged in a nut (not shown)carried by the carriage.

The externally-threaded shank ll) of an intermediate shaft 11 is engagedin a threaded hole formed in the vertical flange 12 of the carriage, theaxis of the shaft being parallel to the axes of the driving and drivenshafts 3 and 4, and the axes of the three shafts lying in the sameplane. Means, such as a nut 13, are provided for locking theintermediate shaft in its axially-adjusted position in the carriage. Theinner end 14 of the intermediate shaft is pointed and is engaged in atapered bearing 15 of a larger angle formed in the concave face 16 ofthe concave-convex intermediate or drive-transmission disc 17, whereforethe latter is capable of a degree of universal rocking movement on thepointed tip 14 of its support.

The contact face 18 of the disc 17 is domed' and in order to obtain thedesired point contact between this face 18 and the peripheral edges ofthe driving and driven discs 5 and 6, and to fulfill certain otherconditions set out below, this contact face should represent the surfaceof revolution of a particular curve. A method of determining this curveis illustrated in Figure 4 which gives the shape of the working face ofthe disc on a section through the center taken at degrees to the face.It also gives the relative position of the pivot point. It is mostimportant that this should be adhered to in order that the point whilstholding thediscs in frictional contact, falls on a line drawn betweenthe points of contact on the peripheral edges of the driver/ drivendiscs with the intermediate disc. This must hold true throughout theadjustment range. Any divergence of the pivot point from this line wouldcause a load on the drive to exert a tipping effort on the intermediatedisc. It is equally important that the point should at all times lie inthe plane between the driver/driven shafts. Unless these conditions arefulfilled true rolling action between the partly in section, of aconparallel, spaced shafts 3 3 discs cannot be secured. It will beapparent from the foregoing that no axial movement of the pivot pointoccurs as the speed ratio is altered, and in those forms of constructionlater to be described wherein the pivot point is replaced by a partspherical seat, sliding of discs and seatings along their shafts islimited to that occasioned by inaccuracies and wear.

The method used in laying-out the curve is very similar to that used inlaying-out a uniform motion cam, dilferences being that it is startedfrom two arbitrary points on a diametral line, which points are spacedapart in accordance with the gap between the points of contact of theintermediate disc with the driver/ driven discs, and is produced foronly a few degrees on either side of this line. The rise per degree ofangular motion is very great. Thus, referring to Figure 4, in laying outthe curve, assuming that H is the center of the tapered bearing in theconcave face of the intermediate disc, a diametral line aa is drawnthrough the center H and on each side of it are drawn threeequi-angularly spaced diametral lines bb, c-c, dd. About the center Hthere is drawn a circle e. of a diameter G which is equal to the widthof'the gap between the points of contact on the adjacent peripheraledges of the driving and driven discs 5 and 6 with the intermediate disc17, and on the outside and inside of this circle, respectively, threeequi-distantly spaced concentric circles f, f, g, g, and h, h, aredrawn. Thus, there. are seven radial lines radiating from the center Hon each side thereof and the points of intersection lettered from j to pand j to p of these lines and the seven concentric circles are pointsupon the curve of the convex working surface 18 of the intermediatedisc. The total cross travel of the carriage carrying the intermediatedisc is equal to the radial distance between the innermost (h) and theoutermost (h) of the said concentric circles and the overall ratio ofthe speed adjustment is equal to the square of the ratio between theradius of the innermost circle and that of the outermost circle.

Whilst in some of the constructions according to this invention the useof springs between adjacent pairs of intermediate discs is unnecessary,the use of at least one spring within a disc assembly on theintermediate shaft is needed in order to compensate for inaccuracies inthe contours of the discs and eventual Wear of the several parts of thedrive.

It is however desirable to keep the curvature of the intermediate discto the minimum consonant with point contact between these and thedriver/driven discs. The hardness, accuracy, and finish of the matingsurfaces will be controlling factors in determining this curvature.

Moreover, as in nearly all practical applications of the drive thoseportions of :the driver/driven discs making contact with theintermediate disc will be in the form of a rounded rather than a squarecorner, a slight modification of the curvature of the intermediate'discswill be needed to offset the change in the point of tangency which takesplace as between one extreme of adjustment and the other. 7

From a consideration of Figures 1 to 3 it will. be apparent that theintermediate disc could equally well be supported on a part-sphericalsurfaceprovidedsuch surface were concentric about the position of. point14. This has been done in a second constructional form of the invention,shown in Figures 5 and 6, which comprises a casing 19 in the front andback'walls 20 and 21 of which two parallel, spaced shafts 22 and 23 arerotatahlyv mounted, one of these shafts being the driving shaft and theother the driven shaft. The cover 20 is, in Figure 5, assumed removed.Between the two shafts-there is an intermediate shaft 24 which isparallel to the other shafts and is supported by ball bearings 25 and26in such manner that its axis lies in the same plane as the axes of thedriving and driven shafts. The driving and driven shafts are providedrespectively with dri i g'and driven discs 29 and 30, eachofwhichissplined for axial'movement along its shaft. The discs are formed withperipheral edges 31 and 32 of substantially circular section. Twointermediate concave-convex discs 33 and 34, having domed surfaces -35and 36, constructed like that of the intermediate discs described above,encircle the intermediate shaft. The intermediate discs are formedrespectively with central, apertured bosses 37 and 38, havingpartspherical outer surfaces 39 and 40 which are rotatably mounted inpart-spherical bearing surfaces 41 and 42 formed respectively in thebody parts of hollow sleeves 43 and 44, the shanks 45 and 46 of whichare slidably arranged upon the intermediate shaft. The peripheral edges31 and 32 of the driving the driven discs 29 and 30 are engaged betweenthe domed contact or working faces 35 and 36 of the two intermediatediscs, and these are thrust into contact with the two peripheral edgesby springs 47 and 48 which surround the intermediate shaft and reactrespectively between the sleeves 43 and 44 and nuts 49 and 50 adjustablythreaded upon the shaft. The part-spherical surface formed on eachintermediate disc is so related to the domed contact face thereof thatthe center of the sphere of which it forms a part is coincident with thedatum point (H Figure 4) of the said face. As a consequence thebehaviour of each intermediate disc will be as if supported at thispoint.

The bearings 25 and 26 of the intermediate shaft 24 are supported inhousings 27 and 28, and in order to obtain the desired lateral movementof the intermediate shaft in the plane containing the axes of thedriver/driven shafts, these housings are each carried by a swinginglinkage 51, 52 pivotally mounted on cross-spindles 53 and 54 parallel toshaft 24. The swinging of the housings 27 and 28 and consequentvariation of the transmission ratio is effected by an arm 55 connectedto spindle 54 and forked at 56 to receive a pin on a nut 57 carried by athreaded spindle 58 having an operating handle 59 at its outer end.

It will be understood that the gear mayinclude a number ofaxially-spaced driving discs all mounted upon the same driving shaft anda number of driven discs all mounted upon the same driven shaft, 21co-operating pair of intermediate discs being associated with eachdriving and driven disc pair.

Thus, as shown in Figure 7, a number of driving discs 60 may be splinedupon a driving shaft 61 and an equal number of driven discs 62 may besplined upon a driven shaft 63 which is'parallelto the shaft 61. Theconstruction comprises an intermediate. shaft 64 which is parallel tothe shafts 61 and 63, the axes of the three shafts lying, as before, inthe same plane.

A number of intermediate disc-pairs are mounted upon the intermediateshaft, each such pair comprising two axially-spaced concave-convex discs65 and 66, the peripheral edges of two of the discs 60 and 62 beingengaged between the domed contact surfaces 67 and 68 of thecorresponding intermediate discs. Each intermediate disc is formed witha part-spherical central aperture 69, the center point of whichcorresponds to the center H shown in Figure 4, the working surface 67and 68. of each pair of discs being formed in accordance with the curveshown in that figure. Within the bore of. each intermediate disc thereis a sleeve 70 which is a sliding fit onthe shaft and which is shapedexternally to form apart-spherical seating 71 for the bore 69 of thedisc. In assembling each intermediate disc and its sleeve, the latter issprung into the bore of the disc Whilst at right angles to the plane ofthe latter until the centers of curvature of the bore and the seatingcoincide, and then rocked back through Pressure of contact between thedriving/ driven discs and the co-operating pairs of intermediate discsis maintained by springs 72 which are fitted between the pairs ofintermediate discs and springs 73 fitted between nuts 74 screwed uponand near to the ends of the intermediate shaft and the adjacentintermediate discs.

In this construction the speed adjustment may be effected by adjustingmechanism comprising swinging links 75 and housings 76 like thoseincluded in the construction shown in Figures and 6, the ends of theintermediate shaft 64 being supported by ball bearings in the housings.

Where it is desired to keep the mechanism as compact as possible anepicyclic type of construction may advantageously be used. In thismanner, the drive may be spread over a large number of elements withoutunduly lengthening the shafts. 7

As shown in Figures 8 and 9, such mechanism may comprise a centralsplined driving shaft 77 on which are slidably mounted a number ofdriving discs 78, each of which is adapted to engage between the workingfaces of the two concave-convex discs 79 of a number of pairs of suchdiscs. Thus, for example, four sets of pairs of cooperating intermediatediscs may, as shown in Figure 8, be arranged around the driving shaft 77and each set carried upon a shaft 80, the four shafts beingangularlyspaced at 90 from each other. At its two ends each shaft 80 ismounted in ball bearings 81 fitted in arms 82 which extend from the endsof a sleeve 83 which is free to rotate about a stud 84, the four studsbeing fixed in a plate 84a (not seen in Figure 8). A plate 85 is carriedat one end of the four studs and is provided internally with a ballbearing 86 for one end of the driving shaft 77 and externally withanother ball bearing 87 upon which a driven drum 88 of cupshape isturnably mounted.

The drive from the driving disc 78 to the sets of pairs of intermediatediscs 79 is transmitted from the latter to axially-spaced driven rings89 which are slidably mounted on longitudinal keys 90 on the inside ofthe drum. Each driven ring is engaged in the space between the discs offour co-planar pairs of intermediate discs.

In order to vary the speed ratio, one end of a control lever 91 ispivotally mounted upon the driving shaft 77 and is coupled by links 92to four of the aforesaid arms 82 which carry the four shafts 80 uponwhich the four sets of intermediate discs 79 are mounted. By pivotingthecontrol lever 91 in one or the other direction the intermediate discs79 are carried towards or away from the driving shaft and the ratio ofthe drive consequently is altered. I

The intermediate discs may be constructed like those included in theabove described constructions shown in Figures 5 and 6 or Figure 7. Itwill be understood that, as with other epicyclic transmissions, the roleof the three main components of the drive i. e. central (sun) discs,intermediate (planetary) disc carrier, and outer rings (annulus) may beinterchanged to suit the requirements of any particular application. Asan example, the drum 88 may be made the driving member, and the shaft 77may be fixed, the plate 84a then becoming the driven member.Furthermore, if a spring is fitted to this plate 84a acting to turn theboss of lever 91 in an anti-clockwise direction a'simple form ofself-regulating drive will be provided, wherein the spring, holding thegear in low ratio, is opposed by centrifugal forces which will begenerated in the intermediate (driven) assembly tending to move it tohigh ratio.

The material most generally suitable for the discs appears to behardened steel, which may be improved by such special processing asnitriding or hard facings such as chrome or Stellite. For light drivesand certain feed motions softer metals or plastics material may be foundsuitable.

What I claim then is:

l. A variable speed friction gear comprising a rotatable driving member,a rotatable driven member spaced from said driving member, and anintermediate disc for transrnitting rotary motion between said drivingand driven members by frictional contact of a face of said disc withboth said members, such intermediate disc having a contact face of domedshape arranged for point contact with each of said members, the contactface of the intermediate" disc defined by a surface of revolutionproduced by a curve representing the intersection of a series of equallyspaced arcs, described about a predetermined center, each in turn withsuccessive, equi-angularly spaced diametral lines through said center.

2. A variable speed friction gear comprising a rotatable driving member,a rotatable driven member spaced from said driving member, anintermediate disc for transmitting rotary motion between said drivingand driven members by frictional contact of a face of said disc withboth said members, such intermediate disc having a contact face of domedshape arranged for point contact with each of said members, the contactface of the intermediate disc being defined by a surface of revolutionproduced by a curve representing the intersection of a series of equallyspaced arcs, described about a predetermined center, each in turn withsuccessive, equi-angularly spaced diametral lines through said centerand means for mounting this intermediate disc for universal movementabout said center, when moved for varying the transmission ratio, withthe points of contact between the driving and driven members and theintermediate disc in the same plane as this center.

3. A gear according to claim 2, characterised by the fact the mountingmeans includes an element whereby the intermediate disc may rock aboutsaid center.

4. A variable speed friction gear comprising a rotatable driving member,a rotatable driven member spaced from said driving member, anintermediate disc for transmitting rotary motion between said drivingand driven members by frictional contact of a face of said disc withboth said members, such intermediate disc having a contact face of domedshape arranged for point contact with each of said members, the contactface of the intermediate disc being defined by a surface of revolutionproduced by a curve representing the intersection of a series of equallyspaced arcs, described about a predetermined center, each in turn withsuccessive, equi-angularly spaced diametral lines through said center,and a pivot rockably supporting said intermediate disc centrally inrelation to the domed contact surface thereof, said pivot beingadjustable along a straight line in a plane containing the points ofcontact with the driving and driven members.

5. A variable speed friction gear comprising a rotatable driving member,a rotatable driven member spaced from said driving member, anintermediate disc for transmitting rotary motion between said drivingand driven members by frictional contact of a face of said disc withboth said members, such'intermediate disc having a contact face of domedshape arranged for point contact with each of said members the contactface of the intermediate disc being defined by a surface of revolutionproduced by a curve representing the intersection of a series of equallyspaced arcs, described about a predetermined center, each in turn withsuccessive,equi-angularly spaced diametral lines through said center,and a movable mounting for said intermediate disc, such mounting havinga partspherical seating receiving a part of interfitting partsphericalcontour on the intermediate disc.

6. A variable speed friction gear comprising a rotatable driving member,a rotatable driven member spaced from said driving member, and a pair ofopposed intermediate discs for frictional contact each with said drivingand driven members to transmit the drive between these latter, each ofsaid intermediate discs having a domed face making point contact withthe driving and driven members the contact face of the intermediate discbeing defined by a surface of revolution produced by a curverepresenting the intersection of a series of equally spaced arcs,described about a predetermined center, each in turn with successive,equi-angularly spaced diametral lines through said center.

7. A variable speed friction gear comprising at least one rotatabledriving disc, at least one rotatable driven disc, a .pair of opposedintermediate discs for frictional contact each with said driving anddriven discs to transmit the drive between these latter, saidintermediate discs havingclomed confronting faces engaging between them,and making'point contact with, a peripheral portion of each of thedriving and driven discs, the contact face of the'intermediate discsbeing defined by a surface of revolution produced by a curverepresenting the intersection of a series of equally spaced arcs,described about a predetermined center, each in turn with successive,equi-angularly spaced diametral lines through said center, a shaft onwhich said intermediate discs are both rockably mounted and axiallyspaced, spring means acting on said intermediate discs to maintain themin'contact with the driving and driven discs and means for effectinglateral adjustment of said shaft for varying the speed-transmissionratio: a

8. A variable speed friction-gear comprising at least one rotatabledriving disc, at least one rotatable driven disc, a pair ofcentrally-apertured, opposed intermediate discs for frictional contacteach with said driving and driven'discs to transmit the drive betweenthese latter, said intermediate discs each having a part-sphericalhear.- ing surface at the aperture thereof, and said intermediate discshaving domed confronting faces engaging between them, and making pointcontact with,-a peripheral portion of each of the driving and drivendiscs, the contact face of the intermediate discs being defined by asurface of revolution produced by a curve representing the intersectionof a series of equally spaced arcs, described about a predeterminedcenter, each in turn with successive, eqni-angularly spaced diametrallines through said center, a shaft for carrying both the intermediatediscs of the said pair, a pair of sleeves on said shaft each having a'bearing surface interfitting and carrying the partspherical bearingsurface of' the corresponding intermediate disc, spring means acting onsaid intermediate discs to maintain them'in contact with the driving anddriven discs, means for effecting lateral adjustment of said shaft forvarying the speed-transmission ratio and shafts parallel to thefirst-mentioned shaft driven and driving discs splined thereon.

and respectively having the 9. A variable speed friction'gear comprisinga driving shaft, a driving disc splined on saiddriving shaft, 21 set ofpairs of axially-spaced cooperating intermediatediscs having domedcontact surfaces'engaging thedriving disc, the contact face of theintermediate discs being defined by a surface of revolution produced bya curve representing the intersection of a series of equally spacedarcs, described about a predetermined center, each in turn withsuccessive, equi-angularly spaced diametral lines through said center,the discs of each pair of intermediate discs being mounted for universalmovement upon an intermediate shaft and the intermediate shafts beingspaced radially'from, and angularly around, said driving shaft,

a cage rotatable around, and concentric with, the driving shaft, adriven ring in said cage and having its inner peripheral edge engagedbetween the contact surfaces of the cooperating pairs of intermediatediscs and means for moving said intermediate discs simultaneouslybetween the peripheral edges of the driving disc and driven ring.

10. 'A gear according" to claim 9, in which each intermediate shaft issupported by pivotally-mounted arms one at least of which is connectedby a link to a common'control member rotatable upon said driving shaft.

11; A variable speed friction gear comprising a driving shaft, aplurality of axially-spaced driving discs splined on said shaft, a setof pairs of axially-spaced cooperating intermediate discs having domedcontact surfaces engaging the driving discs, the contact face of theintermediate discs being defined by a surface of revolution produced bya curve representing the intersection of a series of equally spacedarcs, described about a predetermined center, each in turn'withsuccessive, equi-angularly spaced diametral lines through said center,the discs of each pair of intermediate discs being mounted for universalmove- ;ment upon an intermediate shaft and the intermediate shafts beingspaced radially from, and angularly around, said driving shaft, acage'rotatable around, and -concentric with, the driving shaft, aplurality of driven rings in said cage each having its inner peripheraledge engaged between the contact surfaces of the cooperating pairs ofintermediate discs, and means for moving said intermediate discssimultaneously between the peripheral edges of the driving discs anddriven rings.

12. A variable speed friction gear comprising a rotatable drivingmember, a rotatable driven member spaced from said driving member, anintermediate disc for transmitting rotary motion between such members,said intermediate disc having a contact face of domed shape arranged forpoint contact with one of said members, a

' drive connection between the intermediate disc and the other of saidmembers, the contact face of the'intermediate disc being defined by asurface of revolution produced by a curve representing the intersectionof a series of equally spaced arcs, described about a predeterminedcenter, each in turn with successive, equi-angularly spaced diametrallines through said center and means mounting said intermediate disc foruniversal movement about said center so that movement of the disc variesthe transmission ratio.

References Cited in the file of this patent UNITED STATES PATENTS 33,283Sellers Sept. 10, 1861 7 1,042,720 Richards Oct. 29, 1912 1,699,115Murphy -Jan..15, 1929 1,878,068 Van Berkel Sept. 20, 1932 2,216,642Davis Octll, 1940 FOREIGN PATENTS 920,408 France Jan. 4, 1947 GreatBritain Feb. 5, 1930

